We plan to explore the interactions between coagulation factors and platelets. We will isolate the vitamin K dependent factors from frozen human plasma, iodinate them with 125 I and activate them. We will investigate the mechanism of platelet surface prothrombin activation, the nature of the factor Xa receptor site and the role of platelet coagulation factor V. We will also determine whether factor X is activated on the platelet surface and what reactions take place between factors VII, IX, X. We also plan to develop radioimmunoassays for the activated vitamin k dependent coagulation factors. In our studies of prostaglandin synthesis inhibitors we will determine the sensitivity of arterial cyclooxygenase from human aorta and coronary artery to acetylation by 3H (Acetyl) aspirin compared to enzyme in platelet microsomes. We will investigate the basis for the apparent unique sensitivity of platelet cyclooxygenase to aspirin. We are also carrying out a randomized double bind study to determine the efficacy of 180mg aspirin per day in preventing shunt thrombosis in patients with chronic renal dialysis.